The bottoms from a solvent deasphalting process, hereinafter referred to as "SDA tar", is a high-softening point hydrocarbon of limited utility. Although it does burn, it is difficult to deliver to the furnace in a manageable form. Currently, SDA tar is mixed with petroleum fractions, typically in approximately equal volumes, to form mixtures which are then used as fuel. However, to burn SDA tar by this process, requires the use of higher value materials, such as cracked gas oil, to carry the SDA tar to the burner tip.
A common problem with many fuels is the tendency for low melting slag formation on the heat exchange surfaces of the furnace. Slag is formed as a result of impurities in the fuel. Formation of slag renders many fuels unacceptable for continued usage because excessive slag formation causes severe equipment corrosion and the loss of heating value through reduced heat exchange.
The vast majority of combustible emulsions known in the art are water-in-oil emulsions. In these emulsions oil is the continuous phase and water the discontinuous phase. Usually, the water content is 5-20 wt. %, typically less than 10%. These water-in-oil emulsions have viscosities that are similar to the viscosity of the oil phase. Water-in-oil emulsions made from hydrocarbons with high viscosities require heating to facilitate flow. Hydrocarbons such as bunker fuel oils are sometimes burned as water-in-oil emulsions.
The purpose of the water in these water-in-oil emulsions is to provide secondary atomization of the fuel. Primary atomization is accomplished at the burner nozzle tip. However, with high viscosity fuels, this atomization is insufficient to give good burning characteristics. Secondary atomization, due to the rapid formation of steam from the emulsified water, has been shown to facilitate burning of the hydrocarbon. Typically, these water-in-oil emulsions are formed in-line right before burning, i.e., formed in the same fuel line to the burner.
In contrast, for the hydrocarbon-in-water emulsions of the present invention, water is the continuous phase. The primary function of the water is to reduce the fuel viscosity. It is a fluidizing agent, allowing the emulsion to be handled as a liquid, rather than as a solid. With water as the continuous phase, the viscosity of the fuel is much lower than that of the hydrocarbon alone. Moreover, emulsification of the heavy hydrocarbon phase results in a pre-atomization of the hydrocarbon, which facilitates burning. The net result is a lower flame temperature and lower NO.sub.x emissions.
Hydrocarbon-in-water mixtures are also known in the art wherein heavy hydrocarbons are mechanically ground or fractured at temperatures below the softening point of the heavy hydrocarbon and then mixed with the aide of various chemical additives to produce combustible hydrocarbon-in-water mixtures. The heavy hydrocarbons produced by such processes are composed of particle of irregular shape, displaying the typical conchoidal fracture patterns characteristic of breaking/grinding of a semi-solid glassy material below its softening point.
U.S. Pat. No. 4,537,600 relates to slurries containing water and coarse pitch particles. The pitch is comminuted into particles using a colloid mill operated at conditions of temperature (below 212.degree. F.) and pressure (atmospheric) such that the pitch is contacted with water below the softening point of the pitch. The coarse pitch particles are solidified by contact with water and then further pulverized to form a slurry containing finely pulverized particles.
U.S. Pat. Nos. 4,539,012 and 4,565,546 relate to specific additives for use in pitch-in-water slurries. The slurries are made by combining finely divided pitch in water. These patents contain no teaching of the formation of an emulsion from two liquids whereby a heavy hydrocarbon in water emulsion is made.
U.S. Pat. No. 4,610,695 teaches fuel mixtures containing petroleum residues and pulverized solids such as coal. In examples 1 and 5 the patent specifically teaches the use of a sodium-containing additive (soda) which is detrimental to such fuels in that sodium leads to slag formation.
Petroleum coke is produced at an enormous rate in petroleum refineries. It is a bottoms product of petroleum refining which is now sold for fuel as a solid, or for use as electrical anodes if it has the necessary low sulfur, metals, and volatiles content. If petroleum coke were available as a liquid product, it would make a very attractive fuel because of its high BTU content. Slurries of petroleum coke and/or SDA tar having high solid loadings, (i.e., greater than 50%, preferably greater than 70% solids content by weight) are not usual.
U.S. Pat. No. 4,162,143 teaches water-in-oil emulsions of fuel oil including particulate slurries dispersed in the fuel oil. Of special interest is coal dust. These emulsions are achieved through a blend of cationic, nonionic, and anionic surfactants. Included among the surfactants are alkylesters of orthophosphoric acid.
U.S. Pat. No. 4,375,358 teaches slurry compositions of finely devided carbonaceous solids in water. The compositions include a gelling agent to provide a supporting gel and a viscosity builder to reduce the bleeding of the gel. In the absence of the viscosity builder, water separates and an undesirable phase is produced. Xanthan gum is disclosed as a supporting gel.
U.S. Pat. No. 4,355,651 discloses a method of transporting viscous hydrocarbons through pipes by adding water containing an effective amount of a phosphate ester of a specific block copolymer. The patent is directed toward crude oils, not heavy asphaltic materials.
Canadian Patent 1,142,114 discloses a method of inhibiting asphaltene precipitation from crude oil by adding phosphoric acid partial esters of higher alcohols. Alcohol substituents of less than nine or ten carbon atoms are taught to be ineffective tending to reduce the stability of asphaltenes in the crude oil.
U.S. Pat. No. 4,618,348 discloses a method for utilizing viscous hydrocarbons as fuels comprising forming an emulsion from a viscous hydrocarbon using a water soluble surfactant. The hydrocarbon is characterized as by having a viscosity of greater than 100 centipoise at 150.degree. F.